1. Field of the Invention
The present invention relates to a suspension for supporting a magnetic head slider for use in a rigid magnetic recording disk drive (Hard Disk Drive: hereinafter abbreviated to as HDD).
2. Discussion of the Background
A wiring integrated suspension of the type that is integrally equipped with a part of a wiring structure connected to a magnetic head has recently come into use. The wiring structure is used for connection between the magnetic head and an integrated circuit (hereinafter abbreviated to as preamplifier IC) including a driver circuit for a write signal and a preamplifier circuit for a read signal. Where a magnetoresistive (MR) device is used for the magnetic head, it functions to read a signal, while an inductive device is used to write a signal. Accordingly, four or five wires (two or three wires for reading and two wires for writing) are required in this wiring structure.
FIG. 18 illustrates the wiring integrated suspension installed in the HDD, where the wiring integrated suspension 100 includes a wiring integrated flexure 110 with a magnetic head slider 200 mounted thereon, a load beam 120 for supporting the said flexure 110 and generating a force to press the magnetic head slider 200 against a magnetic disk 300, and a base plate for securing the said load beam 120 to an arm 130 by caulking. In FIG. 18, the base plate is positioned under the arm 130 and therefore cannot be seen. The arm 130 can pivotally be moved around a pivot 140 on a plane in parallel with the magnetic disk 300, so that the magnetic head slider 200 can be moved to a selected track position on the magnetic disk 300. A voice coil motor (VCM) 150 is coupled to a proximal end portion of the said arm 130 so as to drive the arm 130. A terminal (not illustrated) closer to a proximal end of the wiring structure integral with the suspension 100 is connected to a relay FPC (Flexible Printed Circuit) 160 closer to its distal end. The relay FPC 160 is, in turn, connected at its proximal end portion 162 to a print wiring board 170 such as an FPC, on which a preamplifier IC 171 is mounted. FIG. 19 illustrates a wiring integrated suspension of the type that includes a flexure, a load beam and a base plate. In addition to this type of the wiring integrated suspension, there exists a wiring integrated suspension of the type that omits the base plate by directly welding a load beam to an arm.
Such wiring integrated suspensions have been proposed, for example, in Japanese Laid-Open (Kokai) Patent Publication Nos. 8-106617, 8-111015 (U.S. Pat. No. 5,657,186), 9-128728, U.S. Pat. No. 5,680,274, U.S. Pat. No. 5,717,547, etc.
FIGS. 19 and 20 respectively illustrate a perspective view of a wiring integrated suspension 100 of a conventional type, and an exploded perspective view of the wiring integrated suspension of FIG. 19. In these figures, the upper side of the suspension faces the disk. As illustrated in FIGS. 19 and 20, the wiring integrated suspension 100 includes the wiring integrated flexure 110, the load beam 120 and the base plate 180, all of which are welded together at welds 99.
The load beam 120 is provided with a load-bent portion 121, thereby generating the force to press the slider against the magnetic disk.
The flexure 110 includes a wiring structure 111 (hereinafter referred to as flexure wiring structure) integrally formed thereon. The said flexure wiring structure 111 is provided at its proximal and distal ends with terminal pads 111a and 111b, each having a width being wider than a signal line portion 111c extending between the said ends. The terminal pad 111b closer to the FPC is used for connection to a wiring structure (hereinafter referred to as FPC wiring structure) of the relay FPC 160, while the terminal pad 111a closer to the slider is used for connection to a terminal of the magnetic head. The terminal pad 111b closer to the FPC is positioned in parallel with the side of the arm 130 via a terminal bending portion 112 located closer to the proximal end of the flexure 110. A magnetic-head-slider mounting region 113 is provided closer to the distal end of the flexure 110 so as to mount the magnetic head slider thereon. The flexure wiring structure 111 is usually connected to the relay FPC 160 with solder bumps, while the flexure wiring structure 111 is connected to a magnetic head terminal by Au ball bonding.
FIGS. 21(a) and 21(b) respectively illustrate vertical cross sections of the signal line portion 111c of the flexure wiring structure, and of the terminal pads 111a and 111b. As best illustrated in these figures, the wiring integrated suspension 110 includes a stainless-steel substrate 115, a polyimide insulating layer 116 laminated on the disk-facing side of the said stainless-steel substrate 115, a conductor layer 117 laminated on the disk-facing side of the said polyimide insulating layer and a polyimide protection layer 118 surrounding the said conductor layer 117. At each of the terminal pads, the polyimide protection layer 118 is provided with an opening 118a, through which the conductor layer 117 is exposed to the outside.
As illustrated in FIGS. 18 to 21, the wiring integrated suspension of the conventional type includes the flexure wiring structure 111 that is connected to the FPC wiring structure via the terminal pad 111b closer to the FPC and the terminal pad 111b of the relay FPC. In consideration of an assembling error, the terminal pad 111b is usually of a rectangular shape with each side of approximately 0.4 to 0.5 mm.
The capacity of the terminal pads will be discussed hereinbelow. The wiring structure in the wiring integrated suspension employs pairs of wires, each pair including two wires. Accordingly, the capacity of the terminal pads does not represent a capacity Cps between one terminal pad and the stainless-steel substrate, but a capacity Cpad between two terminal pads corresponding to each pair of wires. The capacity directly existing between the two pads is much smaller than the capacity existing between the two pads via the stainless-steel substrate, so that the Cpad can be considered as being Cpad≈Cps/2. Where the terminal pads each are of the rectangular shape with each side of 0.4 to 0.5 mm as described above, providing the polyimide insulating layer 116 having a thickness of approximately 10 micrometers in this arrangement results only in the terminal pad capacity of approximately 0.4 to 0.6 pF.
Such a capacity in a joining region of the flexure wiring structure and the FPC wiring structure invites the following disadvantage. Specifically, the above terminal pad capacity results in mismatching of the impedance at the terminal pads, even if the characteristic impedance of the flexure wiring structure has been matched with that of the FPC wiring structure. This mismatching of the impedance in the wiring structure between the magnetic head and the preamplifier IC invites signal reflection in a mismatching portion, resulting in increase in rate of error occurrence in reading data from and writing data to the magnetic disk by the head. The data transferring speed has recently become higher than ever, so that the signal reflection in the wiring structure poses a serious problem in data transfer at such a high speed (see K. B. Klaassen et al, xe2x80x9cHigh Speed Magnetic Recordingxe2x80x9d, IEEE TRANSACTIONS ON MAGNETICS Vol. 34, No. 4, pp. 1822-1827, 1998).
Specifically, a high-speed data transfer causes a large number of high frequency elements in signals. The mismatching of the impedance at the terminal pads results from the above-described capacity Cpad. The impedance 1/wCpad resulting from the said terminal pad capacity is decreased as the frequency is increased, in which w is an angular frequency 2xcfx80f.
When Zc less than  less than 1/wCpad, in which Zc represents the characteristic impedance of the wiring structure, the mismatching of the impedance at the terminal pads can be disregarded. However, when 1/wCpad is closer to or less than Zc, the mismatching of the impedance at the terminal pads poses a problem.
Among commercially available HDDs at the present day, the highest internal data transfer speed is approximately 200 Mbps. This speed is expected to reach more than 300 to 400 Mbps in the near future, when considering the recent efforts to improve track recording density for data and increase the number of revolutions of the disk. Particularly, shortening the pulse rising/falling time in a writing signal is required, so that the said writing signal contains even frequency elements several times as much as the basic frequency elements. Therefore, when an internal data transfer speed is approximately 300 to 400 Mbps, frequency elements of approximately 1.0 GHz is necessarily taken into consideration. When the signal frequency is 1.0 GHz, the impedance 1/wCpad resulting from the terminal pad capacity becomes 265 to 400 xcexa9. Since the characteristic impedance Zc of the wiring structure of the suspension is generally 50 to 150xcexa9, 1/wCpad increases to such a degree as not to be disregarded for Zc.
The present invention has been conceived in consideration of the above problem. It is an object of the present invention to provide a wiring integrated magnetic head suspension that is capable of preventing the mismatching of the impedance in the joining region between the flexure wiring structure and the FPC wiring structure.
In accordance with the present invention, there is provided a magnetic head suspension including a distal end portion on which a magnetic head slider can be mounted and a proximal end portion adapted for being supported by an arm, which includes:
a flexure including a plate shaped substrate forming at a distal end portion thereof a gimbal portion with a magnetic-head-slider-mounting region, an insulating layer laminated on a magnetic-disk-facing side of said substrate, a conductor layer laminated on said insulating layer for constituting a flexure wiring structure, and an insulative protection layer covering the conductor layer;
a plate shaped load beam including a proximal end portion for being supported by the arm for constituting a suspension in cooperation with the flexure;
an FPC for connection between the conductor layer of the flexure and an external wiring structure;
said FPC including an insulative base layer located on a magnetic-diskfacing side thereof, a conductor layer laminated on a magnetic-disk-facing surface of the insulative base layer, said conductor layer constituting an FPC wiring structure, and an insulative protection layer covering said conductor layer;
the flexure wiring structure including a terminal pad for connection to the magnetic head slider located closer to a distal end of the flexure, a connection portion for connection to the FPC wiring structure located closer to a proximal end of the flexure and a flexure signal line portion for connection between the terminal pad and the connection portion, the connection portion of the flexure wiring structure having a width substantially equal to that of the flexure signal line portion;
the FPC wiring structure including a connection portion for connection to the flexure wiring structure located closer to a distal end of the FPC wiring structure, a terminal pad for connection to an external wiring structure located closer to a proximal end of the FPC wiring structure and an FPC signal line portion for connection between the connection portion and the terminal pad, said FPC signal line portion having a characteristic impedance matching with that of the flexure signal line portion, the connection portion of the FPC wiring structure having a width substantially equal to that of the FPC signal line portion;
the connection portion of the flexure wiring structure having a length determined by multiplying a positional error in joining between the flexure and the FPC by two and adding the result to the width of the connection portion of the FPC wiring structure;
the connection portion of the FPC wiring structure having a length determined by multiplying the positional error by two and adding the result to the width of the connection portion of the flexure wiring structure; and
the connection portion of the flexure wiring structure crossing the connection portion of the FPC wiring structure at right angle and connected thereto.
With the above arrangement, the capacity in a connection portion between the flexure wiring structure and the FPC wiring structure is reduced, so that the signal reflection caused in this portion can be reduced.
The substrate of the flexure may integrally be formed with the load beam.
The connection portion of the flexure wiring structure may be located within a distal end region of the load beam. Therefore, the flexure can be reduced in dimension, thereby reducing the manufacturing cost of the flexure.
The connection portion of the flexure wiring structure may be located within a proximal end region of the load beam. Therefore, it is possible to prevent a load over a load-bent portion of the load beam during a process for joining the flexure and the relay FPC together.
The substrate of the flexure preferably includes a connection stage distally extending from the gimbal portion to connect the connection portion of the flexure wiring structure to the connection portion of the FPC wiring structure within the connection stage. This arrangement omits the necessity to form the flexure wiring structure on the gimbal portion so as to provide improved flexibility in designing the magnetic head suspension. It is also possible to omit the likelihood of damaging the flexure wiring structure even if the gimbal portion is subjected to offset-bending. In addition, the flexure wiring structure can be shortened in length, so that flexures can be manufactured with high yields.
The FPC preferably includes on the protection layer thereof a ground conductor layer which is fixed to a ground electric potential and electrically insulated from the conductor layer of the FPC. With this arrangement, the characteristic impedance of the signal line portion in the FPC wiring structure can remain uniform throughout the lengthwise direction of the said signal line portion, so that the signal reflection in the said signal line portion can effectively be prevented.
The FPC preferably includes the protection layer defining an opening closer to the distal end thereof to expose a surface of the conductor layer of the FPC via the opening, and a solder plated layer covering the surface of the conductor layer exposed via the opening to constitute the connection portion of the FPC wiring structure.
The flexure preferably includes the protection layer defining an opening closer to the proximal end thereof to expose a surface of the conductor layer of the flexure via the opening, and a solder plated layer covering the surface of the conductor layer exposed via said opening to constitute the connection portion of the flexure wiring structure.
The flexure and the FPC preferably include dummy pads respectively formed on portions thereof overlapping to each other, said dummy pads being electrically insulated from the conductor layers of the flexure and the FPC for being connected together by soldering when joining the flexure and the FPC together. The said dummy pads can further strengthen the joining strength between the flexure and the relay FPC, thereby providing improved connection reliability between the flexure wiring structure and the FPC wiring structure.